My question of the day - Flatolet

The flatolet is basically "olet" to be used on flat surface or on the very
large run sizes (where the difference of curvature becomes less and less
significant. As per bonney forge catalogue, the weldolet for run sizes
larger than 36" (DN 1800) will be considered as flatolet.
Please note that one needs to specify this in the purchase order whether
you require flatolet.

I the info below on eng-tips.com

This Bonny Forge chart, calls out some o-let sizes as "flat".

www.bonneyforge.com/specs/branch ... tional.cfm

This table lists which Bonney Forge 'olets can go on what range of headers. For example a standard weight weldolet with a 1" outlet (branch) needs to be ordered based on what the run size is. Since the change in curvature gets less with larger sizes, the same 'olet may be used for multiple run sizes. A 1" 'olet which you'd put on a 6" run pipe would be the same 'olet that you'd put on a 10" run. For a 12" run, though, you'd have to get a different 'olet made to match the larger branch radius (lower curvature). That 'olet will work for up to a 36" branch. Beyond that, the curvature is effectively nil and your radius infinite: In this case, the run is "flat" and that's where the term "flatolet" comes from.

Hope it helps!

Bonny Forge does not use the term "Flatolet" They do use "Flexolet"
(FLATS - A flat Threaded Flexolet for use on welding caps, elliptical heads and flat
surfaces is available.)

WFI also does not have a "Flat-O-Let"
Go here:
www.wfi-intl.com/uploads/docs/WF ... ogv6.2.pdf

Look at the "Consolidation" Chart on page 32.
Purchase a 3" (outlet) x 24" (run) - you will get a 3" that fits on any size from 36" down to 16"